Recent preclinical studies suggest that antidepressants may exert delayed indirect effects on the glutamatergic system. Clinical data suggests that lamotrigine an inhibitor of glutamate release and the NMDA antagonist ketamine may have antidepressant effects. Our group found in two separate studies that the glutamate modulating agent riluzole (inhibitor of glutamate release, and enhancer of AMPA trafficking and glutamate reuptake) was effective in treatment-resistant unipolar and bipolar depression. Together, these data suggest that the glutamatergic system may play a role in the pathophysiology and treatment of depression, and that agents which more directly reduce glutamatergic neurotransmission, may represent a novel class of antidepressants. We are currently testing the efficacy of riluzole in treatment-resistant depression in a double-blind placebo-controlled study in bipolar depression. Patients, ages 18 to 70 years with a diagnosis of bipolar disorder current episode depressed are actively being recruited and randomized to double-blind treated to receive either riluzole (50-200 mg/day) or placebo for a period of 8 weeks. Acute efficacy will be determined by demonstrating a greater response rate using specified criteria. The randomized controlled study is still ongoing and actively recruiting subjects. The study blind has not been broken.